Carburetor



Aplr 30, 1935. A. M. PRENTlss GARBURETOR 'Filed Jan. 25, 1952 ..iinnnl:lanIlil!llllillllllillllllllll/fi V 'lill/Ami;

INV EN TOR. @gaaf/'f7 Af; Pre/72755 BY uf l ATTORNEY atented pr. 30, 1935 UNITED STATES PATENT OFFICE CARBURETOR Augustin M. Prentiss, San Antonio, Tex. Application January 25, 1932, Serial No. 588,756

19 Claims.

This invention pertains to carburetors of the pressure feed, plain tube type, and more particularly has reference to devices for controlling the main air supply so as to facilitate starting, acceleration, and operation at slow speed, especially under heavy loads with wide open throttle.

This invention is an improvement upon the invention disclosed in my United States Patent No. 1,329,309, issued January 27, 1920, and this application is a continuation in part of my copending application, Serial No. 588,755, led January 25, 1932.

In plain tube carburetors of the conventional suction-operated type, the main air intake and Venturi throat must be made large enough to pass sufficient air at the highest operating speed of the motor without reducing the volumetric efflciency of the motor. This necessitates the use of such large air intakes and Venturi throats that at slow speeds, the suction on the main jet is so low that satisfactory operation at such speeds can not be obtained, and various expedients such as separate idling systems and economizers have to be resorted to.

A further dimculty is experienced in eecting rapid acceleration. Since the mixing chamber has such a large and direct communication with the outside atmosphere (through the large size air intakes used), the increase in vacuum due to opening of the throttle becomes almost instantly dissipated, so that little increase in suction is obtained upon the main fuel nozzle. 'I'he term mixing chamber as used in this application designates that part of the main passage which lies between the choke valve and the throttle. This results in diluted mixtures and makes acceleration sluggish and weak.

A still further diiliculty is encountered in slow speed operation, especially under heavy loads with wide open throttle. 'I'his again is caused by lack of suction on the main fuel nozzle due to the large size air intakes and Venturi throats affording unrestricted communication with the outside atmosphere.

Various expedients have been used in an effort to overcome this last difficulty, chief among which are: a variable sized Venturi throat depending on the suction in the mixing chamber; a movable Venturi throat which by shifting its position with reference to the outlet of the main fuel nozzle could be made to exert an increased suction therethese expedients, however, introduced difliculties, in metering the liquid fuel by means of the air component and have been found unsatisfactory.

'I'he principal object of this invention is to overcome the above diiculties'by employing a 5 fixed Venturi throat, whereby accurate metering ofthe liquid fuel by the air component can be secured, and controlling the main air inlet by means of avalve responsive to the vacuum in the mixing chamber, so that as this vacuum increases, 10 the valve opens and correspondingly increases the size of the main air intake.

Another object of this invention is to provide a device for regulating the main air inlet which is responsive to the vacuum in themixing chamber, but which introduces a definite time interval between a sudden increase of vacuum in the mixing chamber and the corresponding increase in the main air inlet, so that during the interval an increased suction is exerted upon the main fuel nozzle thereby securing increased fuel 4feed and rapid acceleration of the motor.

Another object of this invention is tc provide a means of increasing the suction on the main fuel nozzle when the motor is operating at low speed, especially under heavy loads with wide open throttle, thereby automatically increasing the fuel feed and power of the motor under these conditions.

With these and other objects in view which may be incident to my improvements, my invention consists in the combination and arrangement of elements hereinafter described and illustrated in the accompanying drawing which shows in central longitudinal section, a carburetor embodying my improvements.

Referring to the drawing, the reference numeral l denotes the body of a. carburetor having a main air inlet 2, Venturi throat 3, mixing chamber 4, and mixture outlet 5, controlled by a butter- 40 fly throttle valve 6, all arranged as in a conventional plain tube suction-operated carburetor.

Integral with the bottom wall of air inlet 2 is a main nozzle l which consists of an outer liquid fuel tube 8, and a concentric inner compressed air tube 9, both tubes rising to a point slightly above the center of Venturi throat 3 and surmounted by a cap l0 screw-threaded on tube 9 and having a central aperture lila through which' the main jets of liquid fuel and compressed air are discharged into the mixing chamber 4. Tube 8 is connected by a passageway l l and port l2 with a liquid fuel reservoir I3 which receives liquid fuel under a. superatmospheric pressure through an inlet I4 controlled by a. valve l5 which 56 is actuated by a float I6 so as to always maintain a constant liquid fuel level, X-X, in said reservoir.

Port I2 is controlled by a manually adjustable needle valve II which regulates the normal flow of liquid fuel from reservoir I3 to mixing chamber 4.

Two idle fuel feed ports I8 and I9 bestride the throttle 6 (when in closed postion) and are connected by a passageway 20 and metering restriction 2I with tube 8 of nozzle 1.

Air tube 9 of nozzle 'I is connected through a passageway 22 and pipe 23 to a constant pressure compressed air pump, connected to the engine, (not shown) which furnishes air under a constant superatmospheric pressure in quantities proportional to the speed of the engine at all times that the engine is in operation.

The carburetor illustrated in the drawing is of the variable-pressure, fuel-feed-compensating type and, in order to apply the necessary variable pressure to the liquid fuel in the reservoir I3 to cause the flow of liquid fuel through mixing chamber 4 to always bear the desired ratio to the air flow therethrough, I have provided an auxiliary compressed air chamber 24 connected by a passageway 25 with passageway 22, and by another passageway 26, supplementary chamber 21 and port 28 with reservoir I3. The top wall of chamber 24 has la central screw-threaded aperture into which screws a bushing 29.

A central bore 30 in bushing 29 receives a stem 3I which is crew-threaded to a piston 32 adapted to reciprocate with an air tight t in a cylindrical chamber 33. Interposed between piston 32 and cover 34 of chamber 33 is a helical spring 35 which tends to force piston 32 downwardly in chamber 33 against the vacuum of mixing chamber 4 which is transmitted to said chamber by a passageway 36 and metering restriction 36a. Whenever the vacuum in the mixing chamber 4 is greater than the force of spring 35, piston 32 is drawn up to the top of chamber 33 until a lug 37 on piston 32 contacts with cover 34, and conversely, when this vacuum is weaker than spring 35, piston 32 is forced down in chamber 33 until shoulder 38 on stem 3| contacts with the bottom wall of chamber 24.

It will be noted that stem 3| is hollow, closed at both ends, and has in one wall an elongated slot 39 which is of a generally triangular shape with the apex of the triangle at the bottom of the slot. As stem 3I is moved through bushing 29 the area of the slot exposed to chamber 24 is such that the amount of air escaping from chamber 24 through slot 39 is suiiicient to produce in chamber 24 the pressure desired to be exerted upon the liquid fuel in'reservoir I3 for each position of the stem 3 I.

Chamber 33 is provided with a port 39a which is of sufficient size to permit the free escape into the atmosphere of the maximum amount of air which is discharged through slot 39 when stem 5I is in its lowermost position, thus preventing air from collecting in chamber 33 and retarding the movements of piston 32.

The manner in which slot 39 controls the superatmospheric pressure upon the liquid fuel in reservoir I 3 is fully set forth in my copending application Serial No. 588,755, led January 25, 1932,r and since this feature forms no part of the present invention, except that it is operatively associated therewith., it need not be further elaborated here.

Depending from the bottom of stem 3l and integrally attached thereto is a reduced section 40 which passes through an air-tight stuffing box 4I in the bottom wall of chamber 24 and terminates in an eye 42 to which is attached a link 43 which in turn is connected to a butterfly valve 44 pivoted in the main air intake 2, as clearly shown in the drawing.

From the foregoing description, it is apparent that as the stem 3l is moved up and down by piston 32 in response to changes in vacuum in mixing chamber 4, valve 44 will open and close the free opening through main air intake 2. Thus the free opening through the main air intake is varied in accordance with the vacuum in the mixing chamber, and this vacuum, especially in the region immediately adjacent aperture IUa of nozzle 1, determines the suction on the liquid fuel in said nozzle and thus controls the flow of liquid fuel from the nozzle. Thus, as the rate of discharge of the liquid fuel is increased by an increase in the vacuum in the mixing chamber, the free opening through the main air intake is correspondingly increased. But since the piston 32, stem 3|, link 43 and valve 44 have an appreciable inertia, which is augmented byv the air-tight t between the piston 32 and chamber 33, and between the stem 3| and bushing 29, it requires an appreciable interval of time between the instant when the vacuum in the mixing chamber 4 changes and the corresponding change in the position of the valve 44. Thus, if throttle 6 is suddenly kicked open from its restricted position and the high vacuum in the mixture outlet 5 above the throttle is suddenly transmitted to the mixing chamber 4, this vacuum is momentarily held in chamber 4, as the valve 44 is closed and takes a momentary period of time to open in response to the increased vacuum in the mixing chamber 4. During this interval there is produced an increased suction on the main nozzle I which results in an increased fuel flow which greatly facilitates acceleration of the motor. As soon as valve 44 has opened to the extent demanded by the increased vacuum in the mixing chamber, increased communication with the outside atmosphere is established, the vacuum in the mixing chamber falls to that which is maintained under conditions of uniform flow by the degree of opening of the throttle, and conditions of uniform now obtain.

The interval of time required for the valve 44 to respond to a change of vacuum in the mixing chamber is controlled by metering restriction 36a which may be calibrated to secure any inter- Y val desired within certain limits.

As long as valve 44 reduces the opening through air intake 2 so as to make said opening smaller than the opening around the throttle 6, more air leaves mixing chamber 4 than can enter in the same unit of time and therefore, a partial vacuum is set up in mixing chamber 4. This vacuum is proportional to the vacuum existing above the throttle t and the ratio of the opening around said throttle as compared to the opening through the air intake 2. Thus with the opening through air intake 2 equal to that around throttle 6, the vacuum in mixing chamber 4 varies directly and is determined by the vacuum in mixture outlet 5 and also, with the vacuum in mixture outlet 5 constant, the vacuum in mixing chamber 4 varies as the ratio between the openings through air intake 2 and around throttle 6.

From what has just been said, it follows that if air intake 2 is made large enough to pass suf- Cal cient air to meet the requirements of the motor at its highest rated speed and without reducing its volumetric eiiiciency, and this inlet is not reduced at lower speeds, it greatly reduces the vacuum in mixing chamber 4 at such lower speeds until, at speeds just above idling, the vacuum in mixing chamber 4 is not sufficient to draw the A the mixing chamber to' feed the proper amount of liquid fuel at all times and under all operating conditions, and thus obviate the above troubles.

It is to be particularly noted that the valve in the main air inlet is regulated by the vacuum in the mixing chamber and not by the vacuum in the air intake. This is an important difference, as it is the vacuum in the mixing chamber and not that in the air intake that is effective to control the flow of liquid fuel from the main nozzle.

While I have shown and described the preferred embodiment of my invention, I desire it to be understood that I do not limit myself to the constructional details indicated by way of illustration, as these may be varied by those skilled in the'art without departing from the spirit of my invention, or exceeding the scope of the .appended claims.

I claim:

1. In a carburetor having a mixing chamber, an air inlet to said'chamber, a liquid fuel reservoir, means for maintaining a superatmospheric pressure in said reservoir, and means responsive to the pressure in said chamber for varying both the size or" said inlet and the pressure in said reservoir.

2. In a ecarburetor having a mixing chamber, an air inlet to said chamber, a liquid fuel reservoir, means for maintaining a superatmospheric pressure in said reservoir, and means responsive to the pressure in said chamber for varying both the size of said inlet and the pressure in said reservoir inversely as the pressure in said chamber.

3. In a carburetor having a mixing chamber, an air inlet to said chamber, a liquid fuel reservoir, means for maintaining a superatmospheric pressure in said reservoir, and means responsive to the pressure insaid chamber for varying both the size of said inlet and the pressure in said reservoir directly as the vacuum in said chamber. j 4. In a carburetor having a mixing chamber,

means including a nozzle in said chamber for admitting compressed air and liquid fuel thereto, an atmospheric air inlet to said chamber, and means responsive to the vacuum in said chamber adjacent said nozzle for varying the size of said inlet directly as the vacuum in said chamber.

5. In a carburetor having a mixing chamber, means, including a nozzle in said chamber, for admitting compressed air and liquid fuel thereto, an atmospheric air inlet to said chamber, and means retardedly responsive to the pressure in said chamber adjacent said nozzle for varying the size of said inlet inversely as said pressure.

6. In a carburetor having a mixing chamber, means, including a nozzle in said chamber, for

admitting compressed air and liquid .fuel thereto,

an atmospheric air inlet to said chamber, and means responsive to the pressure in said chamber adjacent said nozzle for varying after a desired time interval the size of said.inlet.

7. In a carburetor having a mixing chamber, means, including a-nozzle in said chamber, for admitting compressed air and liquid fuel thereto, an atmospheric air inlet to said chamber, and means actuated byl the vacuum in said chamber adjacent said nozzle for varying the size of said inlet directly as the vacuum in said chamber.

8. In a carburetor having a mixing chamber, means for admitting compressed air thereto, an atmospheric air inlet to said chamber, and means retardedly actuated by the pressure in said chamber for varying the size of said inlet inversely as said pressure.

9. In-a carburetor having a mixing chamber, means for admitting compressed air thereto, an atmospheric air inlet to said chamber, and means actuated by the pressure in said chamber for varying after a desired time interval the size of said inlet inversely as said pressure.

10. In a carburetor having a mixing chamber, means, including a nozzle in said chamber, for admitting compressed air and liquid fuel thereto at all times while the carburetor is in operation, an atmospheric air inlet to said chamber, and a valve responsive to the pressure in said chamber adjacent said nozzle for regulating the opening of said inlet inversely as said pressure.

ll. Ina carburetor having a mixing chamber, means, including a nozzle in said chamber, for admitting compressed air and liquid fuel thereto, an atmospheric air inlet to said chamber, and a valve responsive to the pressure in said chamber adjacent said chamber for varying the size of said inlet inversely as the pressure in said chamber.

12. In a carburetor having a mixing chamber, means, including a nozzle in said chamber, for admitting compressed air and liquid fuel thereto at all times while the carburetor is in operation, an atmospheric air inlet to said chamber, and a valve responsive to the vacuum in said chamber adjacent said nozzle for varying the size of said inlet.

13. In a carburetor having a mixing chamber, means including a nozzle in said chamber, for admitting compressed air and liquid fuel thereto, an atmospheric air inlet to said chamber, and a valve responsive to the ,vacuum in said chamber adjacent said nozzle for varying the size of said inlet directly as the vacuum in said chamber.

14. In a carburetor having a mixing chamber, means for admitting compressed air thereto, an atmospheric air inlet to said chamber, and a valve retardedly responsive to the pressure in said chamber for varying the size of said inlet inversely as said pressure.

15. In a carburetor having a mixing chamber, means, including a nozzle in said chamber, for admitting compressed air and liquid fuel thereto at all times while the carburetor is in operation, an atmospheric air inlet to said chamber, and means responsive to the pressure in said chamber adjacent said nozzle for varying the size of said inlet inversely as said pressure..

16. In a carburetor having a mixing chamber, means, includinga nozzle in said chamber, for admitting compressed air and liquid fuel thereto, an atmospheric air inlet to said chamber, and means responsive to the pressure in said chamber adjacent said nozzle for varying the size of said inlet inversely as the pressure in said chamber.

17. In a carburetor having a mixing chamber, means, including a nozzle in said chamber, for admitting compressed air and liquid fuel thereto at all times While the carburetor is in operation, an atmospheric air inlet to said chamber, and means responsive to the vacuum in said chamber adjacent said nozzle for varying the size of said inlet directly as said Vacuum.

18. In a, carburetor having a mixing chamber, means, including a nozzle in said chamber, for admitting compressed air and liquid fuel thereto, an atmospheric air inlet to said chamber, and means -actuated by the pressure in said chamber adjacent said nozzle for varying the'size of said inlet inversely as the pressure in said chamber.

19. In a carburetor having a mixing chamber,

inlet in direct proportion to the vacuum in said 10 chamber.

AUGUSTIN M'. PRENTISS. 

